Real-time text solutions for multi-party sessions
draft-hellstrom-avtcore-multi-party-rtt-solutions-00

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Last updated 2020-03-28
Replaces draft-hellstrom-mmusic-multi-party-rtt
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Internet Engineering Task Force                             G. Hellstrom
Internet-Draft                                                   Omnitor
Intended status: Best Current Practice                    March 28, 2020
Expires: September 29, 2020

           Real-time text solutions for multi-party sessions
          draft-hellstrom-avtcore-multi-party-rtt-solutions-00

Abstract

   This document specifies methods for Real-Time Text (RTT) media
   handling in multi-party calls.  The main RTT transport is to carry
   Real-Time text by the RTP protocol in a time-sampled mode according
   to RFC 4103 [RFC4103] .  The mechanisms enable the receiving
   application to present the received real-time text media separated
   per source, in different ways according to user preferences.  Some
   presentation related features are also described explaining suitable
   variations of transmission and presentation of text.

   Call control features are described for the SIP environment.  A
   number of alternative methods for providing the multi-party
   negotiation, transmission and presentation are discussed and a
   recommendation for the main ones is provided.  The main solution for
   SIP based centralized multi-party handling of real-time text is
   achieved through a media control unit coordinating multiple RTP text
   streams into one RTP stream.

   Alternative methods using a single RTP stream and source
   identification inline in the text stream are also described, one of
   them being provided as a lower functionality fallback method for
   endpoints with no multi-party awareness for RTT.

   Bridging methods where the text stream is carried without the
   contents being dealt with in detail by the bridge are also discussed.

   Brief information is also provided for multi-party RTT in the WebRTC
   environment.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

Hellstrom              Expires September 29, 2020               [Page 1]
Internet-Draft    Real-time text multi-party solutions        March 2020

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on September 29, 2020.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Centralized conference model  . . . . . . . . . . . . . . . .   5
   3.  Requirements on multi-party RTT . . . . . . . . . . . . . . .   5
   4.  Coordination of text RTP streams  . . . . . . . . . . . . . .   7
     4.1.  RTP-based solutions with a central mixer  . . . . . . . .   7
       4.1.1.  RTP Mixer using default RFC 4103 methods  . . . . . .   7
       4.1.2.  RTP Mixer using the default method but decreased
               transmission interval . . . . . . . . . . . . . . . .   8
       4.1.3.  RTP Mixer with frequent transmission and indicating
               sources in CSRC-list  . . . . . . . . . . . . . . . .   8
       4.1.4.  RTP Mixer using timestamp to identify redundancy  . .  10
       4.1.5.  RTP Mixer with multiple primary data in each packet .  10
       4.1.6.  RTP Mixer indicating participants by a control code
               in the stream . . . . . . . . . . . . . . . . . . . .  11
       4.1.7.  Mixing for multi-party unaware user agents  . . . . .  12
     4.2.  RTP-based bridging with RTT media contents not touched by
           the bridge  . . . . . . . . . . . . . . . . . . . . . . .  14
       4.2.1.  RTP Translator sending one RTT stream per participant  14
       4.2.2.  Distributing packets in an end-to-end encryption
               structure . . . . . . . . . . . . . . . . . . . . . .  15
       4.2.3.  Mesh of RTP endpoints . . . . . . . . . . . . . . . .  15
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